This invention relates to a method of removing foreign materials from developers, and more particularly to a method by which foreign materials responsible for various objections can be removed from magnetic developers for use in magnetic brush developing apparatus widely used in electrophotographic copiers and like machines.
Presently well known as such magnetic developers are single-component developers composed only of an electroconductive magnetic toner, two-component developers comprising a toner of insulating properties and a magnetic carrier admixed therewith, developers in the form of a mixture of two different kinds of magnetic toners, etc. These developers are used for developing the latent electrostatic images on an image bearing surface to toner images while the developer is being circulated through a magnetic brush developing apparatus. As the developer is repeatedly circulated for a prolonged period of time, foreign materials become mingled with the developer.
Typical of such foreign materials are agglomerates of developer particles gradually formed during prolonged use of the developer. (Toner particles in the developer join with one another into agglomerates when subjected to physical forces or heat during the circulation of the developer through the magnetic brush developing apparatus. Usually the agglomerates are approximately 10 times the size of the toner particles.) Typical examples also include fibers of copy paper (generally having a length more than 10 times the diameter of the toner particles) which become mingled with the developer in a gradually increasing amount. The contamination of the developer with copy paper fibers takes place especially markedly in a magnetic brush developing apparatus for transfer-type electrophotographic copiers in which the developer remaining on the surface of the photoconductive member is recovered after the transfer of images to reuse the recovered developer for development.
The presence of the above-mentioned foreign materials in the developer for use in transfer-type electrophotographic copiers and the like causes various problems, such as deterioration of the transportability of the developer itself, irregularities in developed images and blank portions in transferred image areas. With the magnetic brush developing apparatus, therefore, it is very critical to remove the foreign materials from the developer to prevent occurrence of these problems.